It’s easy to notice him, standing 6-foot-4, even taller on skates, and filling out his Islanders uniform with the bulk unbeknownst to many men his age. So 20-year-old Griffin Reinhart spent a good portion of Friday on the Coliseum ice pushing around full-time NHL players, seeking extra advice from coaches and spent first day of on-ice training camp looking as if he belonged.

“I feel really confident,” Reinhart told The Post. “I’m trying to come out here and make an impact, trying to prove that I can play here. I’m feeling good about myself.”

The Islanders’ defense is their distinct shortcoming, at least at this juncture when everything remains strictly on paper. They have two — count ’em, two — established NHL defenseman in Travis Hamonic and Lubomir Visnovsky. There was almost nothing but good signs last season from 23-year-old Calvin de Haan, who picked up top-pair minutes and handled them well. Yet his career service of 52 games is far from a sturdy harbinger.

Behind them, there is the injury-plagued waiver-wire pick-up of Brian Strait, and the smart yet overtly diminutive Thomas Hickey.

There are the five players that have at least a foot in the door for roster positions.

So the eyes go back to Reinhart, the No. 4-overall pick from 2012 who, by way of a shortsighted age restriction for playing in the AHL, spent all of last year with his junior team of the WHL, captaining the Edmonton Oil Kings to the Memorial Cup championship while gaining some sort of experience — how valuable is to be seen.

You see some guys that are rushed [into the NHL], and it works out really well for them, and some guys that are rushed, it doesn’t work out well,” Reinhart said. “As a young kid, I wanted to make the team, and I felt I would be better off up here. But only time will tell [if it was the right decision], and even then, you won’t really know for sure.”“It’s not like there are any free spots,” Reinhart said. “Everybody here is an elite level of defenseman, and they’re all pushing for the same spots.”

Reinhart described himself as a “stay-at-home” defenseman, looking up to the Predators’ Shea Weber (and his $100 million contract) as a model he would like to follow. He spent the summer back in his native Vancouver, skating with his two NHL brothers, Max and Sam, the latter going with the No. 2-overall pick to the Sabres at June’s draft.

Yet now Griffin is back on the cusp of the Islanders’ roster, and it just so happens they are a team that could use someone just like him. Even if the current mood is filled with nothing but confidence.

“I can say, 100 percent, that I’m confident in our defensive corps right now,” Hamonic said, “and we know we all have to up our games. And as a whole, the whole defensive way, we’re going to be better this year.”

It’s not just Reinhart pushing for a spot, either. The other two young blueliners who may be close are Matt Donovan and Kevin Czuczman, who both spent a significant amount of time with the team last year. Donovan, 24, showed streaks of promise (as well as defensive inconsistencies) in his 52 games, while Czuczman, 23, played the final 13 games after signing as a free agent out of Lake Superior State.

“Last year, I put a ton of pressure on myself and I think I was gripping the stick a little too tight,” said Donovan, who also married his middle-school sweetheart, Hallie, while back in their native Oklahoma this summer. “I think this year I just need to relax and play hockey.”

Also fighting for a spot is 25-year-old T.J. Brennan, who has 40 games of NHL service with the Sabres and Panthers and was the AHL Defenseman of the Year last season with the Toronto Marlies. There is also the hulking veteran Matt Carkner (with his hulking $1.5 million contract), to add some grit, if necessary.